Thanks for the updates. I absolutely love these kind of double features, and I always make sure to include several when I'm doing my yearly October/Halloween movie viewing. Here are some vintage feature pairings based on ads I've seen:
The Child (1977) / Axe (1977)
The Texas Chain Saw Massacre (1974) / (The) Silent Scream (1979)
Don't Go in the House (1979) / The Hills Have Eyes (1977)
Embasssy Pictures did many mash ups:
Phantasm (1979) / Psychic Killer (1975)
Phantasm (1979) / The Manitou (1978)
Prom Night (1980) / Phantasm (1979)
Prom Night (1980) / The Fog (1980)

Beyond the Door II (1977) (aka "Shock") / Don't Look in the Basement (1973)
The Dark (1979) / Beyond the Door II (1977) (aka "Shock")
Vampire Playgirls (1971) (aka "The Devil's Nightmare") / Grave Desires (1974) (aka "The Vampires' Night Orgy")
Stanley (1972) / Night of the Lepus (1972)
The House That Dripped Blood (1971) / The Honeymoon Killers (1969)
Thou Shalt Not Kill... Except (1985) (aka "Stryker's War") / Blood Diner (1987)
Alone in the Dark (1982) / The Evil Dead (1981)
The Slumber Party Massacre (1982) / Hell Night (1981)
The Town That Dreaded Sundown (1976) / The Amityville Horror (1979)
Deadly Blessing (1981) / He Knows You're Alone (1980)
Friday the 13th Part 2 (1981) / My Bloody Valentine (1981)
Meatcleaver Massacre (1977) / Final Exam (1981)
Deranged (1974) / Sisters (1973)
The Incredible Melting Man (1977) / Squirm (1976)
Black Belly of the Tarantula (1971) / The Weekend Murders (1970)
The Rocky Horror Picture Show (1975) / Phantom of the Paradise (1974)
Without Warning (1980) / Contamination (1980)
Damien: Omen II (1978) / The Redeemer (1978)
Don't Go in the Woods (1981) / The Hills Have Eyes (1977)
The Island (1980) / The Hearse (1980)
Student Bodies (1981) / Night School (1981)
Evilspeak (1981) / Visiting Hours (1982)
Frightmare (1983) / Curtains (1983)
Friday the 13th Part III (1982) / Parasite (1982)
Some theaters did triple features and more:
Squirm (1976) / They Came from Within (1975) / Frogs (1972)
The Evil Dead (1981) / Xtro (1983) / The Texas Chain Saw Massacre (1974) / Alone in the Dark (1982)
City of the Living Dead (1980) / Hell of the Living Dead (1980) / Funeral Home (1980) / Mausoleum (1983)
The Fog (1980) / Prom Night (1980) / Phantasm (1979) / Death Ship (1980)